Wound resistors with terminal means



June 4, 1968 s. DAVIDSON WOUND RESISTORS WITH TERMINAL MEANS 2 Sheets-Sheet 1 Filed Jan. 10, 1966 SIG,

\ 24 m m 730 I 926 INVENTOR. was ON flr-roeusv June 4, 1968 s. DAVIDSON WOUND RESISTORS WITH TERMINAL MEANS 2 Sheets-Sheet 2 Filed Jan. 10, 1966 l I I4 IIIQ INVENTOR. IEBIG 6pm DAVIDSON I328 BY 47' TOR 5 Y United States Patent 01 hoe 3,387,249 WOUND RESISTORS WITH TERMINAL MEANS Sam Davidson, Los Angeles County, Calif. (23215 Calabash St., Woodland Hills, Calif. 91364) Filed Jan. 10, 1966, Ser. No. 519,760 17 Claims. (Cl. 338298) ABSTRACT OF THE DISCLOSURE Resistor terminations for terminating the effective resistance of a resistance element which has been wound or otherwise spirally disposed about an essentially cylindrical core. An electrically conductive cylindrical member is disposed about the core with at least one portion of an axially inward edge disposed substantially perpendicularly to the spiral direction of the resistance element, with such member edge portion and an electrically exposed end portion of the resisatnce element being disposed in perpendicularly transverse and radially conductive overlay contact relationship with each other at a location along such exposed end portion for elfectively terminating the electrical resistance of the element at such location.

The present invention relates to resistors and, more particularly, to resistor terminations for terminating the effective resistance of a resistance element which has been wound or otherwise spirally disposed about an essentially cylindrical core.

In the past, electrically conductive end caps in the form of cylindrical cups or circular discs have been employed as stable anchoring members intermediary between the resistance element and the terminal leads, the resistance element being joined to the end cap at any point convenient to the random exit of the resistance element from the core or bobbin about which the resistance element is spirally disposed. In the case of film resistors havin a deposited resistance element in the form of a film, the resistance terminations normally are deposited bands of cylindrical or at least partially cylindrical form.

In all such cases, the longitudinally inward edge of the resistance termination member defines a circle or -ring residing in a diametric plane with respect to the core member about which the resistance element is wound or otherwise spirally disposed so that, other than in special cases, the initial contact between the resistance element and the termination member occurs at an oblique intersection therebetween which forms a relatively acute angle. In the case of wire wound resistors, whether of the core or bobbin type, the resistance element may comprise either one electrical resistance wire or a plurality thereof which may be wound in a continuous regular spiral or counter-wound upon itself or themselves in any of the common non-inductive resistance manners, or otherwise, in any event resulting in the random exit of a plurality of resistance wire end portions which, in the case of a single resistance wire, will be at opposite ends of the resistor or, in the case of a plurality of counterwound resistance wires, will be of a plural nature both at the same ends and also at the opposite ends of the resistor. In any event, each resistance wire end portion between the region or point of securement to the end cap and the wound body of the resistance element, such Patented June 4, 1968 as may be caused by vibration, shock, expansion and/or contraction of the resistance element or its physically associated members or both thereof due to temperature variations or otherwise, may cause relative movement or dislocation of the point or region of initial intersection contact between the wire end portion and the end cap termination edge so that, due to the relatively acute angle defined by such intersecting elements, the effective electrical resistance of the resistance element is caused to be varied in an unpredictable and uncontrollable manner from its initially predetermined and preset magnitude or value by a significant proportion. Still further, and of particular importance in those cases where there is a significant length of resistance wire between the effective points of initial intersection contact and securement to the end cap, the dislocation of the wire end portion may be in a radially outward direction whereby intersection contact is lost entirely or, at least, intermittently.

Therefore, it is one of the principal objects of the present invention to provide termination means in a cylindrical type resistor for terminating the elfective resistance of a spirally disposed resistance element in a substantially perpendicular manner so as to eliminate or at least minimize any proportional change in the resistance value which otherwise may occur due to inadvertent relative movement of the resistance element and the termination means.

Another object of the present invention is to provide termination means for effectively stressing the termination portion of the resistance element in a radially outward direction relative to the core member whereby the resistance element tends to urge itself in the radially inward direction of termination contact for improved assurance of such contact.

Accordingly, the present invention provides electrical resistance termination means for use in an electrical resistor having resistance element means disposed in at least one spiral direction about a cylindrical core member between the opposite ends thereof and having a pair of electrically conductive end caps effectively secured to the opposite ends of the core member, each of the end caps having terminal lead means, and the resistance element means having at least one electrically exposed end portion adjacent an end cap in oblique relationship thereto, wherein the termination means of the present invention comprises an electrically conductive cylindrical member disposed about the core member in longitudinally inward and electrically conductive relationship to such end cap and having a longitudinally inward edge including at least one edge portion disposed substantially perpendicularly to said spiral direction, such edge portion and such exposed end portion being disposed in perpendicularly transverse and radially conductive contact relationship with each other at a location along such exposed end portion for elfectively terminating the electrical resistance of the resistance element means at such location. In a preferred embodiment of the present invention, the resistance termination means is an integral portion of the end cap so that the end cap itself is formed to constitute the improved termination means of the present invention. In a still further preferred embodiment of the present invention, the longitudinally inward edge of the termination means comprises a circumferentially spaced plurality of such edge portions whereby such exposed end portion is disposed in counter spiral directions about the core memher so that each of the corresponding exposed end portions of the resistance elements may be disposed in such contact relationship with a random corresponding one of the edge portions as they each exit randomly from their spiral disposition about the core member. As used herein, the term random refers to the situation where, during the course of manufacture, the termination means has been previously immovably secured to the core member prior to the spiral winding of the resistance element about the core member and, thus, the exact location of the point of crossover of the resistance elements exposed end portion relative to the termination means is unknown until the winding is accomplished and the exposed end portion is caused to overlay the termination means at such previously unknown and therefore random location along the longitudinally inward edge of the termination means.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:

FIGURE 1 is a side elevation view of a wire wound resistor showing one embodiment of the end cap termination means in accordance with the present invention;

FIGURE 2 is a fragmentary enlarged perspective view thereof;

FIGURE 3 is an enlarged fragmentary plan view of the termination means of FIGURES 1 and 2, illustrated as though it were laying in a single plane;

FIGURES 4, 5 and 6 are similar in aspect to FIGURE 3 and illustrate modifications of the longitudinally inward edge configurations;

FIGURE 7 is a view similar in aspect to FIGURE 3 showing a modified embodiment wherein the termination edge portions are each provided with a vertical projection;

FIGURE 8 is a fragmentary enlarged sectional view as seen substantially along lines 88 in FIGURE 7;

FIGURE 9 is a fragmentary side elevation view of a wire wound resistor having an end cap termination in accordance with the present invention, illustrating another embodiment having a vertical projection termination;

FIGURE 10 is a fragmentary enlarged sectional view as seen substantially along line 1010 in FIGURE 9;

FIGURE 11 is a side elevational view of a bobbin-type wire wound resistor showing one embodiment of the end cap termination in accordance with the present invention, FIGURE 12 being a fragmentary enlarged perspective view thereof;

FIGURE 13 is a side elevation view, partly broken away and sectioned, of a film type resistor showing one embodiment of the termination means in accordance with the present invention; and

FIGURE 14 is a view, similar in aspect to FIGURES 3-7, of the resistance termination means shown in FIG- URE 13.

In the drawings, the same reference numerals refer to the same or similar elements; however, for convenience and clarity of description, similar elements often are referenced by the same numeral bearing prefix digits corresponding to the figure member of the particular embodiment or modification.

Referring initially to FIGURES 1, 2 and 3, there is seen a wire wound resistor, indicated generally at 10, having a non-conductive core member 12 about which is spirally wound a wire resistance element 14 in any standard manner well known in the art. A pair of conductive end caps 16 and 18 are disposed about the respective ends of the core member12 and secured thereto in any convenient manner, such as by a force fit, for assuring relative immobility. Each of the end caps 16 and 18 is provided with a respective terminal lead 20 and 22 of any standard type and configuration for connection into an electrical circuit in the well-known manner. The end caps 16 and 18 being identical to each other and disposed oppositely to each other so as to present effectively mirrorimage configurations whereby the exposed opposite wire end portions 24 and 26 approach their respective end caps 16 and 18 from the effectively same oblique or spiral direction, only the one end cap 16 will be described in further detail in connection with the embodiment illustrated in FIGURES 1-3 as well as the other embodiments.

The end cap 16 is provided with an edge 28 facing longitudinally inwardly toward the resistance element 14. In the prior art, such edge 28 would be circular and reside in a diametric plane relative to the core member so that the wires exposed end portion 24 would form an oblique angle of intersection with such circular edge as the wire crossed over the edge. However, in accordance with the present invention, the edge 28 is serrated or otherwise formed as by a circumferentially continuous plurality of notches whereby the edge 28 consists of a plurality of edge portions 30 each disposed substantially perpendicularly to the oblique or spiral direction of exit ofthe wire end portion 24 from its main bodys disposition about the core member 12.

Each of the edge portions 30 has the same angular disposition relative to the circular periphery of the core 12 whereby the wire end 24 of the resistance element 14 may be readily disposed in right-angle intersecting relationship to the edge portion 30 as the wires exposed end portion 24 is extended onto the end cap 16 for termination thereon. A welded joint 32 or any other convenient means of securement is employed to securely engage the terminus or end of the wire to the end cap 16 whereby the physical and electrical region 34 of intersecting contact and engagement between the end portion 24 and end cap 16 at the edge portion 30 is relatively fixedly determined. Any one of the edge portions 30 may be employed, depending upon the point of random exit of the wire end portion 24 from its spiral disposition about the core member 12. I

As seen in FIGURE 3, a plurality of resistance wires may be disposed about the core member so as to have their corresponding plurality of exposed end portions 24 exiting in the same spiral direction for overlaying the termination member end cap 16 at different intersection contact points 34 of corresponding edge portions 30.

Although the alternate edge portions 36 of the longitudinally inward edge 28 are illustrated as being at right angles to the intersection edge portions 30, any convenient configuration thereof may be employed as long as they do not interfere with the desired relationship of the wire end portions 24 with the edge portions 30.

Referring to FIGURE 4, there is illustrated a modified embodiment of the end cap serrations wherein the edge portions 430 and 436 are disposed at right angles to each other comparable to the previously described edge portions 30 and 36 but the alternating intersections 42 and 44 of such edge portions are smoothly rounded or radiused for ease and simplicity in manufacturing thereof insofar as finishing operations are concerned.

Referring to FIGURE 5, there is seen another embodiment of the end cap configuration in accordance with the present invention wherein the longitudinally inward edge 528 of the end cap termination means 516 is provided with a spaced plurality of axially parallel semi-circular projections or tabs 50 whereby a plurality of resistance wire end portions 24 may be disposed in resistance termination relationship to the end cap 516 by intersection at 534 with any convenient relatively radially inwardly disposed portions of the projection 50 which offers a perpendicular intersection edge portion 530 to the wire end portions 24, whether such end portions exit in the same or counter spiral directions.

Referring to FIGURE 6, there is seen a further modification wherein the longitudinally inward edge 628 of an end cap termination 616 has a plurality of edge portions 630 each of which is adapted to receive and electrically terminate an exposed wire end portion 24 in one spiral direction, and has a plurality of opposed or counter spiral direction edge portions 630' adapted to receive and electrically terminate a resistance element wire end 24 which has been wound about the core in the opposite or counter spiral direction. Each pair of edge portions 630 and 630 together with a recessed edge portion 60, defines a longitudinal notch in the edge 628 of the end cap 616 whereby the plurality of axial notches defines alternating pairs of edge portions 630 and 630, such edge portions being equi-angularly disposed in mirror image relationship to each other about a radial longitudinal plane through the core.

Referring to FIGURES 7 and 8, there is seen a modification of the embodiment illustrated in FIGURES 1-3 with an upward or radially outward projection 70 adjacent and parallel to the edge portion 730 and substantially smoothly continuous therewith whereby the resistance element wire end portion 24 is deflected upwardly or outwardly at its region of intersection with the edge portion 730 and then downwardly to its welded region of end contact at 32 with the end cap 716. Thus, the wire end 24 is deflected and forced to assume a relatively increased stressed disposition at its region of intersection with the end cap 716 at the edge portion 730 whereby an even greater assurance of mechanically rigid and electrically positive contact is obtained.

For convenience and clarity of illustration and description, the upper radial projections have been shown and described only in connection with FIGURES 7 and 8; however, it now should be clear that such projections are equally applicable to the embodiments illustrated in FIG- URES 1-6, 11 and 12.

Referring to FIGURES 9 and 10, there is seen another variation in accordance with the present invention of an end cap termination utilizing the vertical projection termination concept of FIGURES 7 and 8 wherein the end cap 916 does not have a serrated or otherwise configured edge, but, rather, has merely an annular vertical projection 970 adjacent to and continuous with the axially inward termination edge 928 for achieving the positive termination effects of the projection 70 in FIGURES 7 and 8 but without the perpendicular termination effects of the previously described embodiments.

Referring to FIGURES l1 and 12, there is seen a bobbin-type wire-wound resistor 1110 utilizing the end cap termination effects previously describe in connection with FIGURES 1-3. A resistance element 1114, normally covered with electrical insulation material, is wound about a non-conductive bobbin core 1112 in any standard manner well known in the art, including counter-wound upon itself so that its opposite wire end portions 1124 and 1126 exit in the same rotational direction as they pass over the enlarged core end 52. The conductive end cap 1116 is primarily cylindrical and secured as by press fit onto the end portion 52 of the core member. The radially outer surface 54 of the end cap 1116 is notched along its longitudinally inward edge 1128 to form only partial radial depressions therein while achieving the termination edge portions 1130 along a radially outer portion of the edge 1128, thus leaving a circular edge portion 1128' for assuring mechanical securement of the end cap 1116 to the core.

Referring to FIGURES 13 and 14, there is seen a filmtype resistor 1310 wherein a cylindrical core 1312 is provided with a spirally formed resistance element 1314 which may be formed of deposited carbon or other material in any manner well known in the art and having a spiral groove 60 formed therein as by grinding or any other well known manner. A cylindrical termination element 1316 in accordance with the present invention is disposed about an end of the resistor 1310 and has a configuration such that an edge portion 1330 of the longitudinally inward edge 1328 is disposed in a perpendicular direction to the spiral direction of orientation of the resistance element 1314 for termination of the effective resistance thereof. In this embodiment, the termination members 1316 and 1318 are separate members from the end caps 62 and 64 for convenience of application and adjustment, the end caps 62 and 64 being secured as by 6 press fit engagement about the termination members 1316 and 1318.

It should be noted that a particular advantage resides in the embodiment illustrated in FIGS. 13 and 14 which is not necessarily attendant to the previously described embodiments. Due to the fact that the current flow through the body of a spirally wound resistance element is along such spiral direction, the prior art terminations along a circular edge transversely diametric to the core member cause such termination edge to be disposed obliquely relative to such spiral direction and, thus, obliquely to the direction of current flow. When the termination contact is not at a point but rather along a line, as is the case with a film type resistor, the prior art termination contact is along an oblique line; since the termination means has negligible resistance (effectively zero resistance compared to that of the resistance element), the current path through the obliquely terminated portion of the resistance element tends to be concentrated at the closest portion or end of the termination line rather than to flow through the greater resistance of the remainder of the resistance element toward the farthest portion or end of the termination line. As a consequence of such highly concentrated current density at the physically closest region of the termination line, the current density or distribution is unequal not only along the termination line itself but also through the adjacent region of the resistance element. Applicant has discovered that the effects of such point or region-concentrated current density and the converse unequal current density or distribution cause an effect known as noise. By terminating the film-type resistance element in the above-described transversely perpendicular manner, such effects are avoided. It should be noted that the wire wound embodiments of the present invention partake of the same advantages in those cases wherein wire is employed having a rectangular cross-section or similar configuration such that the termination contact occurs along a line rather than a point.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changesand modifications may be made without departing from this invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. In combination with an electrical resistor having resistance element means consisting of at least one resistance wire and disposed in at least one spiral direction about a cylindrical core member between the opposite ends thereof and having a pair of electrically conductive end caps effectively secured to the opposite ends of the core member, each of the end caps having terminal lead means, and the resistance element means having at least one electrically exposed end portion adjacent an end cap in oblique relationship thereto with an end effectively secured to said end cap, electrical resistance termination means comprising:

an electrically conductive cylindrical member disposed about said core member'in longitudinally inward and electrically conductive relationship to such end cap and having a longitudinally inward edge including at least one edge portion disposed substantially perpendicularly to said spiral direction, said edge portion and said exposed end portion being disposed in perpendicularly transverse overlay and radially conductive contact relationship with each other at a location along such exposed end portion for effectively terminating the electrical resistance of the resistance element means at such location.

2. The invention defined in claim 1 wherein:

said resistance termination means is an integral portion of said end cap.

3. The invention defined in claim 1 wherein:

said resistance element means consists of a plurality of resistance wires each disposed in the same spiral direction about the core member;

each of said wires has one such exposed end portion with said end thereof effectively secured to said end cap; and

said longitudinally inward edge comprises a circumferentially spaced plurality of such edge portions whereby each of said exposed end portions is disposed in said contact relationship with a random corresponding one of said edge portions.

4. The invention defined in claim 3 wherein:

said resistance termination means is an integral portion of said end cap. I

5. The invention defined in claim 4 wherein:

each of said edge portions includes an upper radial projection adapted to form a radially curved reversal in direction of such exposed end portion for improved assurance of physical and electrical engagement of such exposide end portion with said edge portion.

6. The invention defined in claim 1 wherein:

said resistance element means consists of at least two resistance wires disposed in counter spiral directions about the core member;

each of said wires has one such exposed end portion with said end thereof efl ectively secured to said end cap; and

said longitudinally inward edge comprises a circumferentially spaced plurality of such edge portions alternately disposed substantially perpendicularly to a corresponding one of said spiral directions wherebyeach of such exposed end portions is disposed in said contact relationship with a random corresponding one of said edge portions.

7. The invention defined in claim 6 wherein:

said resistance termination means is an integral portion of said end cap.

8. The invention defined in claim 7 wherein:

each of said edge portions includes an upper radial projection adapted to form a radially curved reversal in direction of such exposed end portion for improvedrassurance of physical and electrical engagement of such exposed end portion with said edge portion 9. The invention defined in claim 1 wherein:

said longitudinally inward edge is formed to comprise a circumferentially spaced plurality of semicircular tabs each having one of said edge portions whereby such exposed end portion is disposed in said contact relationship with a random one of said edge portions.

10. The invention defined in claim 9 wherein:

said resistance termination means is an integral portion of said end cap.

'11. The invention defined in claim 10 wherein: each of said edge portion includes an upper radial projection adapted to form a radially curved reversal in direction of such exposed end portion for improved assurance of physical and electrical engagement of such exposed end portion with said edge portion. 12. The invention defined in claim 1 wherein: said longitudinally inward edge is formed to have a circumferentially spaced plurality of serrations each having one of said edge portions whereby such exposed end portion is disposed in said contact relationship with a random one of said edge portions. 13. The inventon defined in claim 12 wherein: each of said edge portions includes a upper radial projection adapted to form a radially curved reversal in direction of such exposed end portion for improved assurance of physical and electrical engagement of such exposed end portion with said edge portion. -14. The invention defined in claim 12 wherein: said resistance termination means is an integral portion of said end cap. 15. The invention defined in claim 12 wherein: said resistance element means consists of at least two resistance wires disposed in counter spiral directions about said core member; each of said wires has one such exposed end portion with said end thereof effectively secured to said end cap; and

each of said serrations has two of said edge portions 1 each disposed substantially perpendicularly to a corresponding one of said spiral directions whereby each of such exposed end portions is disposed in said contact relationship with a corresponding one of said edge portions of a random one of said serrations.

16. The invention defined in claim 15 wherein:

said resistance termination means is an integral portion of said end cap.

17. The invention defined in claim 16 wherein:

each of said edge portions includes 'an upper radial projection adapted to form a radially curved reversal in direction of such exposed end portion for improved assurance of physical and electrical engagement of such exposed end portion with said edge portion.

References Cited German printed application No. 1,173,578 to Mayer,

July 1964, in class 338-302.

LEWIS H. MYERS, Primary Examiner.

E. GOLDBERG, Examiner. 

